The Effect Of Salinity On The Antioxidant System Of Black Sea Bream And The Comparison Of Fatty Acid Composition Between Hybrid Sea Bream And Its Parent

Black porgy(Acanthopagrus schlegli)is broad-salt seafood fish species,because of its delicious meat and strong resistance to diseases,currently it has become one of the important economic species of marine aquaculture in China.Up to date,the studies on the salinity adaptability of black seabream mainly focus on the macro level of black seabream,such as juvenile and young fish survival at different salinities,pond aquaculture of black seabream in low salinity,etc.There are also some literature on the crossbreeding of black porgy,and indicated that some hybrid progeny also shown some dominant traits.Nevertheless,scanty report about the fatty acid content and composition of the offspring of black porgy and red sea bream.Therefore,this study investgated the activities of four antioxidant enzymes(Superoxide dismutase,SOD;Catalase,CAT;Glutathion S-transferases,GST;Glutathione peroxidases,GPX)and the expression patterns of two SOD genes and proteins under different salinity treatments.Furthermore,the comparative analysis of fatty acid content and composition in black porgy,red sea bream,and hybridprogeny is performed.The main results are as follows:(1)Antioxidase activity and SOD gene and protein expression of black snappers at different salinitiesThe activities of four kinds of antioxidant enzymes(SOD,CAT,GPX and GST)and the expression patterns of SOD genes and proteins in three tissues(liver,gill and kidney)of black porgy under different salinities(5,15,25,35 and 45 salinity)were detected.The results show that the activities of four antioxidant enzymes and the expression level of SOD genes and proteins in black porgy are different in different salinity treatment groups,among which the enzyme activity and protein expression levels in the high salt group(35,45 salinity)are more significant influenced by salinity stress than that in the low salt groups(5,15).Moreover,stress response to salinity occurred mostly in 6 h and 12 h.Furthermore,in natural seawater(25 salinity),the antioxidant enzyme activities also varied slightly over time,but overall they are relatively stable.In addition,the antioxidant enzyme activity and SOD gene expression pattern of black porgy is inconsistent.The activity and protein expression level of black porgy SOD shows significant changes with the change of salinity,while the expression of SOD gene show low level.The expression level of SOD gene in 15 salinity is significantly higher than that of other experimental groups.The expressions of CuZnSOD and MnSOD are not significantly changed or even slightly inhibited when salinity was too high(salinity 35)or too low(salinity 5).In this study,the antioxidant enzyme activity analysis of the black porgy under different salinities treatment shown that this species has a strong tolerance to salinity,of which low salt tolerance is stronger than the high salt group.The enzyme activity was restored to its normal survival level by autoregulation within 24h,but up-regulated or down-regulated by SOD gene and protein did not return to normal within 120h.This provides a reference for the study of the relationship between salinity and antioxidant properties.It also provides a certain theoretical basis for the low salinity pond culture of black sea bream.(2)Crude fat content and fatty acid composition analysis of black porgy,red sea bream and hybridprogenyIn this study,Soxhlet extraction is used to determine the contents of crude fat and fatty acid in the liver,muscle and fish bones of four species of sea bream,Pagrosomus major,Acanthopagrus schlegeli and their hybrids.The specific components of fatty acids are analyzed by gas chromatography.The experienmental results show that the positive and anti-hybrid offspring inherited the advantages of the both parents sea bream,the fat content is significantly higher than the parent black porgy,and the most significant in the liver.The composition of saturated fatty acid is basically consistent between the offspring and the parents.Moreover,several fatty acids that are not detected in parents,such as C22:0,C24:0,which have been detected in the hybridprogeny.The result indicate that the fatty acid composition of the hybridprogeny is richer than the both parents.The unsaturated fatty acid composition of hybridprogeny and black seabream parents is nearly the same,especially in the liver composition.The results could provide a theoretical basis for the selection of suitable breeding environment for black seabream and hybrids breeding,and further understand antioxidant molecular regulation mechanism of the different salinity on the black porgy.